The present invention relates in general to power supply systems and is more particularly related to AC power supply and battery back-up systems for telecommunications systems.
In many applications where T1 access devices are installed at a customer premise, there is a need for a separate AC power supply to power the device as well as an auxiliary battery back-up system to protect the operation of critical communications devices that are connected to the T1 in the event of a power failure. There are a wide variety of conventional AC power supplies and back-up systems available for this purpose. A block diagram of a typical combination AC power supply and battery back-up system 100 used in the prior art is shown in FIG. 1. The system 100 includes a conventional rectification and power conditioning section 101 having two outputs as shown. The first output (output 1) is connected to an electronic system (such as a T1 access system) to provide power to the system during normal operation. The first output is also linked to a monitoring and battery back-up relay control circuit 102. The monitoring/control circuit 102 monitors the first output to determine if the voltage being supplied to the electronic system is within specified parameters for the electronic system and, if not, sends a signal to the normally open relay circuit 103 to switch the battery 104 into the power circuit to the electronic system. The second output (output 2) is used to maintain a charge on the battery 104 and is connected to the battery 104 through a battery charge limiting circuit 105 and a battery disconnect relay 106. A battery monitoring circuit 107 monitors the condition of battery 104 and opens the normally closed relay 106 when the battery electrical parameters deviate from normal.
There are several weaknesses in the typical prior art system 100 as illustrated in FIG. 1. First, because the rectification/conditioning section 101 uses two separate outputs to supply load current to the telecommunications system and to supply charging current to the battery, the complexity (e.g., parts count) of the section is increased, which can add to the overall expense of the system 100. In addition, because the power supply is designed to have enough power capability to fully power the load and charge the battery simultaneously, the system 100 is actually capable of supplying more power than necessary when the telecommunications system draws less than its peak power requirements; something that occurs with telecommunications systems that provide ringing power to multiple voice phone lines.
Second, the separate charge limiting circuit 105 also increases the component count and power dissipation of the system 100. Third, the battery back-up function of the prior art system 100 is not entirely automatic because the battery 104 is not connected to the electronic system during normal operation. Rather, the monitoring and relay circuit 102 must be used to close the relay circuit 103 when an abnormal condition is detected at output 1.
Thus, there is a need for an improved and lower cost AC power supply and battery back-up system to power T1 interface devices as well as other communications equipment.
Accordingly, one object of the present invention is to provide an AC power supply and battery backup system having a single output.
Another object is to provide an AC power supply and battery back-up system that operates without a separate charge limiting circuit.
A further object of the present invention is to provide an AC power supply and battery back-up system that includes a battery that is automatically connected to the telecommunications system if the AC power supply fails to supply power to the telecommunications system.
Another object of the present invention is to provide an AC power supply and battery back-up system that takes advantage of the fact that the average power requirements for a telecommunications system are significantly less than the peak power requirements over a given time period.
These and other objects are satisfied by an AC power supply and battery back-up system that includes a power-limited, single output, AC/DC power supply, and a battery connected to the telecommunications system. The AC/DC power supply includes a full bridge rectifier connected to a flyback converter circuit and is designed to provide the peak power required by the telecommunications system. When the operating power requirements for the telecommunications system drop below the peak power output by the AC/DC power supply, the power supply uses the difference to supply charging power to the battery. Since the battery is already connected to the telecommunications system, it automatically supplies operating power to the telecommunications system if the AC input voltage to the power supply is lost. The AC/DC power supply also includes a peak current limiting circuit to limit the output power of the power supply when it is charging the battery. Finally, in one embodiment designed to protect the battery, the battery back-up system includes a battery monitoring circuit for monitoring the battery voltage and a relay connected between the battery and the telecommunications system for disconnecting the battery from the telecommunications system when the battery voltage drops too low.